Of all the ways in which the U.S. and the Soviet Union compete, none is more dangerous than their rivalry in the development and deployment of strategic nuclear weapons. Of all the ways in which the two countries conduct diplomacy with each other, none is more important than strategic arms control, the cooperative effort by which these otherwise competing superpowers try to regulate their rivalry and keep it from getting out of hand. Of all the ways in which Soviet-U.S. relations have declined over the past year, none is more...